# 3.5 while 循环语句与 for 语句
在这一节中，我们请自行回顾 Chap1 里使用 while 和 for 循环的例子。
上述说明可以看成是一个惯例，下面两个具体使用 while 和 for 的例子证实了这一点。
### 3.5.1 while 循环
```c
while (条件) {
// 循环体，当条件为真时执行
}
```
可以回看 1.2 节，温度转换的例子。
{% code title="3.5.1 fahr-cel-while.c" lineNumbers="true" %}
```c
#include
int main()
{
int fahr, cel;
int lower, upper, step;
lower = 0; // 最低温度
upper = 300; // 最高温度
step = 20; // 步长
fahr = lower;
while (fahr <= upper)
{
cel = 5 * (fahr - 32) / 9;
printf("%d\t%d\n", fahr, cel);
fahr = fahr + step;
}
return 0;
}
```
{% endcode %}
```
➜
0 -17
20 -6
40 4
60 15
80 26
100 37
120 48
140 60
160 71
180 82
200 93
220 104
240 115
260 126
280 137
300 148
```
### 3.5.2 for 循环
```c
for (初始化; 条件; 更新) {
// 循环体，当条件为真时执行
}
```
可以回看 1.3 节，温度转换的例子。
{% code title="3.5.2 fahr-cel-for.c" lineNumbers="true" %}
```c
#include
int main()
{
int fahr, cel;
int lower, upper, step;
lower = 0; // 最低温度
upper = 300; // 最高温度
step = 20; // 步长
for (fahr = lower; fahr <= upper; fahr = fahr + step)
{
cel = 5 * (fahr - 32) / 9;
printf("%d\t%d\n", fahr, cel);
}
return 0;
}
```
{% endcode %}
使用 for 的惯用法：
```c
for (i=0;i
♻️ 我们可以尝试把一个 for 循环转化成一个 while 循环，也可以倒过来。
### 3.5.4 for 的几个惯用法 idioms
从 0 向上加到 n-1：
```c
for (i=0;i=0;i--)
```
从 n 向下减到 1:
```c
for (i=n;i>0;i--)
```
---
# Agent Instructions: Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.
Perform an HTTP GET request on the current page URL with the `ask` query parameter:
```
GET https://labspc.gitbook.io/cnippets/chap3.-kong-zhi-liu/3.5-while-xun-huan-yu-ju-yu-for-yu-ju.md?ask=
```
The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.
Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.
